6lo P. Thubert, Ed.
Internet-Draft Cisco
Updates: 4944 (if approved) R. Cragie
Intended status: Standards Track ARM
Expires: April 15, 2017 October 12, 2016
6LoWPAN Paging Dispatch
draft-ietf-6lo-paging-dispatch-05
Abstract
This specification updates RFC 4944 to introduce a new context switch
mechanism for 6LoWPAN compression, expressed in terms of Pages and
signaled by a new Paging Dispatch.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Updating RFC 4944 . . . . . . . . . . . . . . . . . . . . . . 3
4. Page 1 Paging Dispatch . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6.1. Consuming Dispatch Types . . . . . . . . . . . . . . . . 5
6.2. New Column in Dispatch Type Registry . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The design of Low Power and Lossy Networks (LLNs) is generally
focused on saving energy, which often is a very constrained resource.
Other constraints, such as memory capacity and duty cycle
restrictions on LLN devices, usually derive from that primary
concern. Energy is often available only from primary batteries that
are expected to last for years, or is scavenged from the environment
in very limited amounts. Any protocol that is intended for use in
LLNs must be designed with a primary focus on saving energy, which is
a strict requirement.
Controlling the amount of data transmission is one possible means of
saving energy. In a number of LLN standards, the frame size is
limited to much smaller values than the IPv6 maximum transmission
unit (MTU) of 1280 bytes. In particular, an LLN that relies on the
classical Physical Layer (PHY) of IEEE 802.15.4 [IEEE802154] is
limited to 127 bytes per frame. The need to compress IPv6 packets
over IEEE 802.15.4 led to the 6LoWPAN Header Compression [RFC6282]
work (6LoWPAN-HC).
As more and more protocols need to be compressed, the encoding
capabilities of the original dispatch defined in the 6lo adaptation
layer framework ([RFC4944],[RFC6282]) becomes saturated. This
specification introduces a new context switch mechanism for 6LoWPAN
compression, expressed in terms of Pages and signaled by a new Paging
Dispatch mechanism.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The Terminology used in this document is consistent with and
incorporates that described in Terms Used in Routing for Low-Power
and Lossy Networks [RFC7102] and Terminology for Constrained-Node
Networks [RFC7228].
3. Updating RFC 4944
This draft adapts 6LoWPAN while maintaining backward compatibility
with IPv6 over IEEE 802.15.4 [RFC4944] by introducing a concept of a
"parsing context" in the 6LoWPAN parser, a context being identified
by a Page Number. This specification defines 16 Pages.
Pages are delimited in a 6LoWPAN packet by a Paging Dispatch value
that indicates the next current Page. The Page Number is encoded in
a Paging Dispatch with the Value Bit Pattern of 1111xxxx where xxxx
is the Page Number, 0 to 15, as described in Figure 1:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1|1|1|1|Page Nb|
+-+-+-+-+-+-+-+-+
Figure 1: Paging Dispatch with Page Number Encoding.
Values of the Dispatch byte defined in [RFC4944] are considered as
belonging to the Page 0 parsing context, which is the default and
does not need to be signaled explicitly at the beginning of a 6LoWPAN
packet. This ensures backward compatibility with existing
implementations of 6LoWPAN.
The Dispatch bits defined in Page 0 by [RFC4944] are free to be
reused in Pages 1 to 15. This specification allocates some values in
Page 1 in Section 4 and leaves the rest open for future allocations.
Values opened by this specification in Page 1 to 14 are to be
assigned for new protocols whereas Page 15 is reserved for
experimentations.
Note: This specification does not use the Escape Dispatch, which
extends Page 0 to more values, but rather allocates another Dispatch
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Bit Pattern (1111xxxx) for a new Paging Dispatch, that is present in
all Pages, including Page 0 and Pages defined in future
specifications, to indicate the next parsing context represented by
its Page Number. The rationale for avoiding that approach is that
there can be multiple occurrences of a new header indexed by this
specification in a single frame and the overhead on an octet each
time for the Escape Dispatch would be prohibitive.
A Page (say Page N) is said to be active once the Page N Paging
Dispatch is parsed, and remains active until another Paging Dispatch
is parsed.
4. Page 1 Paging Dispatch
This specification defines some special properties for Page 1,
detailed below:
The Dispatch bits defined for LOWPAN_IPHC by the Compression
Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks
[RFC6282] are defined with the same values in Page 1 so there is
no need to switch context from Page 1 to Page 0 to decode a packet
that is encoded per [RFC6282].
Mesh Headers represent Layer-2 information and are processed
before any Layer-3 information that is encoded in Page 1. If a
6LoWPAN packet requires a Mesh header, the Mesh Header MUST always
be placed in the packet before the first Page 1 Paging Dispatch,
if any.
For the same reason, Fragment Headers as defined in [RFC4944] MUST
always be placed in the packet before the first Page 1 Paging
Dispatch, if any.
The NALP Dispatch Bit Pattern as defined in [RFC4944] is only
defined for the first octet in the packet. Switching back to Page
0 for NALP inside a 6LoWPAN packet does not make sense.
As a result, there is no need for restoring the Page 0 parsing
context after a context was switched to Page 1, so the value for
the Page 0 Paging Dispatch of 11110000 may not actually occur in
those packets that adhere to 6LoWPAN specifications available at
the time of writing this specification.
5. Security Considerations
The security considerations of [RFC4944] and [RFC6282] apply.
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6. IANA Considerations
6.1. Consuming Dispatch Types
This document allocates 16 values from the Dispatch type field
registry that was created for [RFC4944]. The allocated values are
from 11 110000 through 11 111111 and represent Page Numbers 0 through
15 as discussed in this document.
6.2. New Column in Dispatch Type Registry
This document extends the Dispatch type field registry that was
created for [RFC4944] and updated by the [RFC6282], by adding a new
column called "Page".
This document defines 16 Pages, "Page 0" to "Page 15".
The content of the incumbent registry is assigned to "Page 0".
This document also places in the registry associated to Page 1 the
Dispatch type field values that are allocated for LOWPAN_IPHC by
[RFC6282]. These values range from 01 100000 through 01 111111 and
have the same definition in Page 1 as they do in Page 0; as a result,
the registry entries for Page 0 and Page 1 are an exact overlap in
this range.
Values ranging from 00000000 to 11101111 in Page 15 (that is all of
Page 15 but the space used for Page switch) is reserved for
experimentations and shall not be assigned.
The resulting registry may be represented as a table as follow
(partial):
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pattern | Page | Header Type | defining document |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 0 | NALP | RFC 4944 |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 00xxxxxx | 1..14 | free | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ N/A |
| | 15 | reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 0 | ESC | RFC 6282 |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 01000000 | 1..14 | free | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ N/A |
| | 15 | reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 0..1 | LOWPAN_IPHC | RFC 6282 |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 011xxxxx | 2..14 | free | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ N/A |
| | 15 | reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1111xxxx | 0..15 | Page switch | This |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Integrating the new Page column
Future assignments in these registries are to be coordinated via IANA
under the policy of "Specification Required" [RFC5226]. It is
expected that this policy will allow for other (non-IETF)
organizations to more easily obtain assignments.
7. Acknowledgments
The authors wish to thank Tom Phinney, Thomas Watteyne, Tengfei
Chang, Martin Turon, James Woodyatt, Samita Chakrabarti, Jonathan
Hui, Gabriel Montenegro and Ralph Droms for constructive reviews to
the design in the 6lo Working Group.
8. References
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8.1. Normative References
[IEEE802154]
IEEE standard for Information Technology, "IEEE std.
802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low-Rate
Wireless Personal Area Networks".
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<http://www.rfc-editor.org/info/rfc4944>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<http://www.rfc-editor.org/info/rfc6282>.
8.2. Informative References
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <http://www.rfc-editor.org/info/rfc7102>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
Authors' Addresses
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Pascal Thubert (editor)
Cisco Systems
Building D - Regus
45 Allee des Ormes
BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 4 97 23 26 34
Email: pthubert@cisco.com
Robert Cragie
ARM Ltd.
110 Fulbourn Road
Cambridge CB1 9NJ
UK
Email: robert.cragie@gridmerge.com
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